Hard aluminum alloy



United States Patent 3,531,337 HARD ALUMINUM ALLOY Ichiro Kawakatsu, 31Yayoicho, Itabashi-ku, Tokyo, Japan No Drawing. Filed Dec. 26, 1967,Ser. No. 693,100 Claims priority, application Japan, Dec. 26, 1966, 41/84,560 Int. Cl. C22c 21/00 US. Cl. 14832.5 4 Claims ABSTRACT OF THEDISCLOSURE An aluminum alloy having high hardness and abrasionresistance elevated by subjecting an alloy containing 2.6- 7.8% zinc,and 0.6-3.8% magnesium as principal additive elements to 'be theprincipal aging hardeners, in addition thereto, O.21.2% of each of iron,nickel and cobalt of transition metal of Group IV, 0.11.2% manganese,0.5% or below chromium, and at the same time containing ODS-1.2%zirconium (in some cases, replaced in part with titanium or hafnium) ofGroup IV, ODS-0.3% boron which is a metalloid, and 0.050.85% silicon andthe remainder of aluminum to nitriding treatment while the alloy ismolten state, and then to the solution treatment at a temperature 450490C. as being cast or after worked, thereafter applying the aginghardening to the alloy at a temperature of 85 to 130 C. and in somecases, before the hardness reaches the maximum point in the agingtreatment, further applying plastic work to the alloy.

The aluminum alloys which are widely used as construction materials arelight in weight as well as considerably strong. However, the alloys havedefects in actual use thereof in such points that their hardness are farlower than those of iron and steel materials or other nonferrousmaterials such as copper alloys, etc. Namely, when compared with othermetallic materials, the aluminum alloys are relatively soft, andtherefore the surfaces of the alloys are not only readily scratched, butalso deformed or worn away. Accordingly they cannot be used as screwnuts, and other parts of machines.

Table 1 shows the comparison of hardness between typical constructionalmetals and practically used high tension aluminum alloys.

TABLE 1.-COMPAR1SON OF HARDNESS OF TYPICAL CONSTRUCTIONAL MATERIALS ANDPRACTICALLY USED ALUMINUM ALLOYS As shown above, the hardness of hightension aluminum is in general limited to 120-135, while the hardness ofcopper alloys is much higher than this. The hardness of carbon steelbecomes also considerably higher than this when it is subjected to heattreatment. Therefore, for the actual use of the aluminum alloys, theirlow hardness is extremely disadvantageous.

The object of the present invention is to obtain an aluminum materialwhose hardness is higher than any other commercial aluminum alloys byspecial treatments to 3,531,337 Patented Sept. 29, 1970 which thechemical ingredients of the aluminum alloy is subjected, and to make thealuminum material applicable as such screws, viz nuts, springs, andother parts of machines that require high abrasion resistance propertyas those of iron and steel.

The chemical ingredients contained in the present alloys are 2.67.8%zinc and 0.6-3.8% magnesium as the principal additive elements whichmainly act as the components of age hardening. In addition to these, thepresent alloys contain 02-12% of each of iron and nickel of transitionmetals of Group IV of the Periodic Table, 0.1-1.2% manganese, and 0.5%chromium. At the same time, the alloys contain ODS-1.2% zirconium ofGroup IVa (in some cases, this being replaced in part with titanium 0rhafnium), 0.0050.3% boron which is a metalloid, and 0.050.85% silicon,and the remainder of aluminum.

The characteristics points in treating the alloys of the presentinvention are in that the molten metal is kept at elevated temperatureafter the melting of the alloys and in the nitrogenization of alloywhich is carried out by passing nitrogen or a nitrogen-containing gas,for example, ammonium into the molten alloy to react with each other orby reacting a nitrogen-containing compound such as anammonium-containing compound or a nitrate, so that zirconium of Group IV(in some cases, titanium or hafnium are included) is dispersion hardenedas a zirconium nitride. Boron, also, forms in part boron nitride, andpromotes the strengthening of dispersion.

Among other additive elements, iron, nickel and cobalt of Group IV ofthe Periodic Table form intermetallic compounds in the aging aluminumalloys. Further, in the case of single use of these hardening elementsfor the purpose of reducing the concentration thereof in the solidsolution, 1% addition thereof is destructive, the simultaneous additionof at least two elements, however, hardly damaging the aging hardness.

Manganese has an effect to improve the fineness of grain size of crystaland toughness together with chromium, and since chromium increases thecorrosion resistance, against especially stress corrosion, the additionof a small amount of chromium is effective. Also, the addition of asmall amount of silicon which already exists in the raw metalcontributes to the age hardening.

Thus, the present invention is an alloy melt prepared by adding theabove-mentioned various elements to the aging aluminum-zinc-magnesiumsystem, and subjecting the system to the nitriding treatment. Thegreatest characteristics of the present invention is to produce an alloyhaving hot and cold workabilities and at the same time such a highhardness produced by solution treatment and age hardening (T treatment)or the work hardening thereafter that has never been observed.

The examples of alloys of the present invention will he illustrated asTable 2.

TABLE 2.COMPOSITIONS IN EXAMPLES OF ALLOYS OF THE PRESENT INVENTION ZnMg Ni Zr Fe Co B Si Mn Example 1 5. 0 2. 0 0. 4 0. 35 0. 4 0. 006 0. 40. 6 Example 9 5.0 2.0 0.2 0.35 0.8 0.6 0. l 0.18 0. 3

3 above-mentioned solution treatment, and artificial aging are as shownin Table 3.

TABLE 3.AGING I'IARDENING IN THE EXAMPLES OF ALLOYS OF THE PRESENTINVENTION Micro Vickers hardness Aging time (Chr.)

As shown in Table 3, the hardness reaches about 180 in the aginghardening conditions, which is the highest hardness in the conventionalaluminum alloy. This hardness matches the hardness of hardenedphosphorus bronze or that of medium carbon steel. Furthermore, when theaging hardening of the alloy of the present invention is stopped beforethe highest possible hardness is obtained by this treatment, it ispossible to produce an amazingly high hardness of Vickers hardness 200or more by applying about 50% cold work to this alloy. For example, thealloy of a Vickers hardness of 205 is obtained in Example 1, and aVickers hardness of 201, in Example 2, these hardness being about twiceof that imparted to duralumin 2017, and matching the hardness of copperalloy naturally or even that'of iron material.

The present alloy is, as explained above, an alloy having such a highhardness that ever seen as a wrought aluminum alloy having workabilityand as aluminum base alloy treated with T treatment. The present alloyalso shows an extremely high hardness as casting material, and isfurther improved by solution and aging treatments (T treatment) afterthe alloy was cast.

The composition of the example and the aging hardness under suchtreatment condition as described above are as shown in Table 4.

TABLE 4.-CO1\IPOSITION AND AGING HARDNESS IN THE EXAMPLE OF CAST ALLOYOF THE PRESENT INVENTION Example 3 (Metal mold, cast): Zn, 5.0; Mg, 2.0;Ni,

0.55; Zr, 0.35; Fe, 0.7; Cr, 0.1; B, 0.1; Si, 0.35; Mn, 0.7.

Aging hardness (Micro-Vickers hardness: same as above) Cast condition:127; Solution treatment: 84; Aging time (hr.): 18,157;40,169;45, 181.

The alloy of the present invention shows, as illustrated above, aconsiderable hardness (a Vickers hardness of 127) under castingcondition. By the T treatment, the hardness of the present alloy reachesa Vickers hardness which is as high as 180, so that the aluminum alloyexcellent in abrasion resistance is obtained as a casting product.

The aluminum alloy high in hardness to which the present inventionrelates demonstrates excellent properties produced by such a compositionas was shown in the previous example, and by various treatments suitedfor the composition.

As to the behaviors of elements of the composition, zirconium (in somecases, titanium or hafnium being included) and boron become, as alreadyexplained above, dispersion particles by forming nitrides thereof by thesolution treatment, and perform the action of dispersion strengtheningby blocking the move of dislocation line. In this occasion, the suitableamount of zirconium or a metal of its group is 0.051.2%, and the amountof boron, 0.0050.3%. When the amount of any element is smaller that thelower limit, no effect is observed, while when the amount of the elementexceeds the upper limit, the workability is damaged or the alloy perhapsbecomes fragile.

Transition metal iron, nickel and cobalt of Group IV of the PeriodicTable have very little solid solubility in aluminum, concentrate aroundcrystalline grain boundary and strengthen the neibourfood of grainboundary by increasing the dislocation density, and promote the Workhardenings. The single use of these metals is in some cases, asdescribed above, destructive to the age hardening, while thesimultaneous use of at least two elements of these do not damage the agehardening, so that these elements are added simultaneously for thesereasons. In this case, the suitable amount of each of these ingredientsis in the range of 0.21.2%. When the amount is smaller than the lowerlimit, there is no practical effect, and when the amount exceeds theupper limit, the corrosion resistance is damaged, toughness, also, beingreduced.

Chromium and manganese of the transition metals of Group IV check thedeterioration of the grain boundary by making the crystalline grainsfiner similarly to the action of iron with an effect that corrosionresistance is increased. Both elements are very useful and especiallywhen chromium is contained at 0.5% or below, the ingredient is effectiveparticularly to casting alloys. 01-- 1.2% manganese has an effect ofimproving malleability. Silicon promotes the age hardening, and,similarly to the above-mentioned iron and other transition metals, hasan effect of checking the deterioration of the grain boundary. Theaddition of a large amount of silicon, however, damages workability. Itssuitable amount is in the range of ODS-0.88%.

What I claim is:

1. An aged aluminum alloy product high in hardness and abrasionresistance characterized by elevating the hardness of an alloycontaining 2.6-7.8% zinc, 0.63.8% magnesium, 0.21.2% iron, 0.2-1.2%nickel and/or cobalt, 0.1-1.2% manganese, 0.5 or below of chromium,0.05-1.2% of at least one element from the group consisting ofzirconium, hafnium and titanium, said element being combined withnitrogen in the product to form dispersed nitrides; 0.0050.3% boron, atleast a part of which is combined with nitrogen in the product to formdispersed nitrides, and 0.03-0.85% silicon, and the remainder ofaluminum, said product having been made by subjecting said alloy to anitriding treatment while in the molten state, and then to a solutionheat treatment at a temperature in the range of 450490 C. as cast orafter working and thereafter to an aging treatment at a temperature ofto C. to produce a high hardness, and, in some cases, before the maximumhardness is obtained in the aging treatment, further subjecting thealloy to plastic working.

2. An alloy product of claim 1 comprising 5.0% Zn, 2.0% Mg, 0.4% Ni,0.35% Zr, 0.4% Fe, 0.006% B, 04% Si and 0.6% Mn.

3. An alloy product of claim 1 comprising 5.0% Zn, 2.0% Mg, 0.2% Ni,0.35% Zr, 0.8% Fe, 0.6% Co, 0.1% B, 0.18% Si and 0.3% Mn.

4. An alloy product of claim 1 comprising 5.0% Zn, 2.0% Mg, 0.55% Ni,0.35% Zr, 0.7% Fe, 0.1% Cr, 0.1% B, 0.35% Si and 0.7% Mn.

References Cited UNITED STATES PATENTS 2,793,949 5/1957 Imich 75-138 X3,171,760 3/1965 Vernam et al 75146 X 3,180,728 4/1965 Pryor et al.75l38 3,262,762 7/1966 Bechtold 75l38 X 3,304,209 2/1967 Anderson et al.75146 X 3,332,773 7/1967 Dudas 75146 3,468,658 9/1969 Herald et al.75135 CHARLES N. LOVELL, Primary Examiner US. Cl. X.R.

